Relief devices of the type commonly known as rupture discs have been utilized in industry for many years to provide a safety mechanism to relieve excess pressure from an overpressurized system or vessel in a reliable manner. The rupture disc is most frequently placed in a vent or a pressure vessel or the like so as to prevent flow of fluid through the vent until the disc ruptures. Through the years, numerous improvements have been made in the rupture disc concept in order to reduce the cost and improve the reliability of the disc.
A specific type of disc normally referred to as a reverse buckling rupture disc has also been utilized for a number of years and functions under the principle that a disc dome is formed in the disc which is positioned in the vent such that the disc dome points toward or faces the pressure side of the vent, i.e., the convex side of the disc dome faces the internal region or upstream side of the vent where pressurized fluid is likely to produce an overpressure that would be dangerous or destructive if not relieved. One advantage of reverse buckling type discs is that systems being protected by the discs can be operated at pressures relatively close to the bursting pressure of the disc without producing fatigue and failure which occurs in many forward acting bursting discs when operated for long periods of time near the rated bursting pressure of such devices. When fluid pressure reaches a preselected pressure for which the disc dome was designed to rupture, the disc dome starts to collapse, i.e., the column or arch of the disc dome on one side thereof starts to buckle. It is believed that as the arch on one side of the disc dome starts to collapse, a buckling-type wave typically propagates across the surface of the disc dome to the opposite side of the disc dome where total collapse eventually occurs. This buckling wave tends to create a whiplash effect on the opposite side of the disc dome so that the disc dome at this location is rather violently urged in the direction to which the concave region of the disc dome faces (i.e., the downstream side of the vent).
One disadvantage of some conventional reverse rupture discs is that if they are damaged during handling, installation, or otherwise, they can buckle at a pressure below the rated pressure for the disc. In some cases, the disc will buckle at a pressure of between 40 and 80 percent of the rated pressure. For example, if the rated pressure is 100 psi, a damaged disc may buckle at between 40 and 80 psi. While the reverse rupture disc may buckle or reverse at such pressures, it will not necessarily open at these pressures and once a reverse rupture disc becomes inverted, it thus acts as a forward acting rupture disc which will rupture at a higher pressure than the initial buckling pressure. For such discs the rupture pressure may be as much as three to ten times the rated pressure.
Another disadvantage of some conventional reverse rupture buckling devices is that they are incapable of reversing and rupturing at low bursting pressures. Bursting pressures are generally defined relative to the size of the disc. For example, 15 psig would be a low bursting pressure for a 2 inch diameter disc made of stainless steel. Conventional limitations to achieving low bursting pressures have been twofold (1) causing the rupture disc dome to reverse at a low pressure, and (2) being able to open the rupture disc at the lower reversal pressures. As previously mentioned, some damaged, conventional reverse buckling rupture discs may reverse at a low pressure but not rupture at that pressure. Also, it is more difficult to rupture conventional reverse buckling rupture discs at low pressures where the media is noncompressible (e.g., a liquid). This is because a noncompressible media such as a liquid does not impart the same dynamic energy to the dome during collapsing as a compressible media does.
Many of the conventional reverse buckling rupture discs include knife blades positioned on the concave side of the disc dome which are normally in spaced relationship to the disc dome, but which are engaged by the disc dome upon buckling. The knives cut the disc dome typically into quarter sections. Knife blade assemblies for reverse buckling rupture discs however add substantially to the cost of such discs and are subject to failure due to corrosive activities of the fluids within the vent system, damage during handling or simply because a mechanic forgets to install the knife assembly which in normal discs results in disc bursting pressures which are many times the rated pressures of such discs. It has, therefore, been a goal of the rupture disc industry to produce a disc of the reverse buckling type which does not include knife assemblies, but which is highly reliable.
One reverse buckling disc, which was specifically designed to rupture without use of knife blades, incorporates the concept of placing grooves, scores or etchings, especially in a criss-cross or circular patterns on concave or convex faces of a reverse buckling rupture disc dome. A disc dome of this type can be seen in U.S. Pat. No. 3,484,817 to Wood. In the Wood device, the rupture disc dome buckles, reverses and fractures along the lines of weakness produced by the grooves so as to form petals which are held to the remainder of the rupture disc assembly.
There is also a problem in some conventional systems with portions of the rupture disc being entrained with the fluid being relieved. Pieces of rupture discs can cause damage to pumps and the like if they are allowed to freely break away from the remainder of the rupture disc assembly upon rupture. Therefore, it is important that the rupture disc dome or petals of the rupture disc dome remain intact after rupture and that they remain attached to the remainder of the disc.
There has been a continuing desire in the rupture disc industry to produce new types of reverse buckling rupture discs which have properties that make them especially suitable for specific purposes, more cost efficient, and/or make the disc more reliable. In particular, new reverse buckling discs are desired which will function at lower burst pressures, and reliably open at or below the rated burst pressure if damaged, without the need for knife blades for cutting the disc on reversal, and yet which will remain attached after rupture to minimize possible damage to the system protected by the disc.